1. Field of the Invention
This invention relates to a mechanism for actuating the hook and feed dog and for adjusting the stitch length in portable sewing machines.
2. Description of Related Art
Portable sewing machines are employed to sew closed with chain stitch seams packages, sheets, and paper or canvas bags e.g. for packaging potatoes, granulated fodder, and so forth. Such machines are subjected, accordingly, to serve operating environments brought about, among other factors, by the nature of the materials handled, a dusty environment, the high sewing speeds sought, and so forth. These machines, moreover, are required to be reliable in operation and as light in weight as feasible.
With prior machines, chain stitching is of the plain type, that is, the chain is formed by a sequence of individual loops which are intertwined progressively one after another, the chain being formed by means of a needle having an associated hook set to swing reciprocatingly around the needle over an angle of about 150.degree.-160.degree.. A wider angle of rotary reciprocation of the hook is not presently achievable owing to structural limitations inherent in prior art designs. The hook is driven by a driveshaft by a cam, the latter having two spaced-apart detents cooperating with two detents, also spaced apart, which are rigid with a hook carrier shaft.
Such a construction is disclosed in Italian Pat. No. 829,852. Prior machines further include a mechanism for actuating the feed dog for advancing the material being sewn. Such mechanisms require a large number of components, and accordingly, are bulky and heavy. This results in increased overall dimensions of the sewing machine, and attendant heavier weight thereof. Prior sewing machines are also provided with a mechanism made up of several parts for setting the sewing stitches to different lengths. This brings about, in turn, similar problems to the above. With prior machines, the large number of moving parts also pose wear problems and tolerance problems. The net result is noisy operation and the need for frequent lubrication. In practice, moreover, it has been found that accidental breakage of some plain chain stitches can often result in running of the adjacent stitches and consequently in the bag or the like being opened and its contents, e.g. granulated fodder, lost. This is specially likely to also occur while handling, shifting, or shipping such bags and the like, as well as on account of faulty seams.